The invention relates to a method and means of detecting solid particles in a fluid flowing through a conduit.
The invention relates in particular to a method and means for counting the number of particles that pass through a pre-determined area of the cross-section of the conduit and for counting the particles and optionally differentiating in the size of the particles when these are of one and the same composition.
Solid particles, such as sand grains, are often entrained in a flowing fluid that is being recovered from an underground formation, such a formation containing hydrocarbons. The sand grains entrained with the fluid (such as gas and/or liquid hydrocarbons) can cause erosion of the conduits in the well, as well as the pipelines and fluid treating installations on the surface. In order to take timely counter-measures, an early warning is required of the presence of those amounts of sand grains that can be expected to cause damage of the recovery equipment in the well or on the production site.
A method and equipment for detecting solid particles in a flowing fluid is known already, wherein at least part of the particles carried by the flowing fluid impinges against a microphonic probe. Each impact is recorded separately, since the impacts are distinguishable from background noise. Also, a method and apparatus for grain detection in a flowing fluid is described in U.S. Pat. Nos. 3,816,773; 3,841,144; 3,854,323 and 3,908,454 in which the grains activate transducer means responsive to acoustic energy to generate a signal representative of said energy, wherein a frequency range around 700 kHz of the signal is held to be representative of the kinetic energy of the total amount of grains striking the transducer means and a frequency range around 100 kHz of the signal is held to be representative of the background noise.
Further, a method and means are known for detecting individual solid particles that are being carried in a particular flow area of a flowing fluid. Herein, the grains impinge on a piezoelectric transducer. The peak value of the resulting electric output signal is detected in a pulse height discriminator after a suitable amplification of this signal. When the peak value exceeds a pre-set discrimination level, a standard output pulse is produced with a length that is greater than the typical duration of the impact signal. The number of standard pulses is counted in a pre-determined period. At a given velocity, the grain diameter can be estimated from the peak amplitude of the impact response, and a differentiation can be made between different ranges of grain sizes which will lead to a grain-size distribution of the grains that pass through a given area of the cross-section of the conduit over a given period.